U.S. patent number 7,436,879 [Application Number 09/453,276] was granted by the patent office on 2008-10-14 for spread communication system and mobile station thereof.
This patent grant is currently assigned to Fujitsu Limited. Invention is credited to Nobuhisa Aoki, Hiroaki Iwamoto, Takaharu Nakamura.
United States Patent |
7,436,879 |
Iwamoto , et al. |
October 14, 2008 |
Spread communication system and mobile station thereof
Abstract
A system and apparatus including a mobile station for use in a
spread communication system having a spread signal on a particular
channel for establishing synchronization. The particular channel
for establishing synchronization existing on a plurality of
frequencies. The mobile station includes a receiving unit receiving
the plurality of frequencies; a measuring unit measuring a strength
or a correlation value of the spread signal of the particular
channel for each of the plurality of frequencies received by said
receiving unit; and a synchronization establishing unit
establishing synchronization based on the measured strength or
correlation value of the spread signal.
Inventors: |
Iwamoto; Hiroaki (Kanagawa,
JP), Aoki; Nobuhisa (Kanagawa, JP),
Nakamura; Takaharu (Kanagawa, JP) |
Assignee: |
Fujitsu Limited (Kawasaki,
JP)
|
Family
ID: |
11520714 |
Appl.
No.: |
09/453,276 |
Filed: |
December 2, 1999 |
Foreign Application Priority Data
|
|
|
|
|
Jan 7, 1999 [JP] |
|
|
11-002128 |
|
Current U.S.
Class: |
375/150 |
Current CPC
Class: |
H04B
1/7075 (20130101); H04B 1/7083 (20130101); H04W
48/16 (20130101); H04W 52/24 (20130101); H04W
88/08 (20130101); H04W 56/00 (20130101) |
Current International
Class: |
H04B
1/00 (20060101) |
Field of
Search: |
;375/150,147,148,343,354,355,364 ;370/335,337,347 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ahn; Sam K
Attorney, Agent or Firm: Myers Wolin, LLC
Claims
What is claimed is:
1. A mobile station for use in a spread communication system having
a particular channel for establishing synchronization, the
particular channel for establishing synchronization existing on a
plurality of carrier frequencies, comprising: a receiving unit
receiving the plurality of carrier frequencies; a measuring unit
measuring a strength or a correlation value of a spread signal on
the particular channel for each of the plurality of carrier
frequencies; a storing unit storing information about the
particular channel having a signal strength or correlation value
for each of the plurality of carrier frequencies; and a
synchronization establishing unit establishing synchronization on
one of the carrier frequencies of the plurality of carrier
frequencies based on the information stored in said storing unit,
wherein said synchronization establishing unit selects for
establishing synchronization a carrier frequency based on the
information stored in said storing unit.
2. The mobile station according to claim 1, further comprising a
comparing unit comparing the signal strength or correlation value,
which is measured by said measuring unit, with a predetermined
threshold value, and wherein said storing unit stores information
about the particular channel having the signal strength or
correlation value which is larger than the predetermined threshold
value.
3. The mobile station according to claim 1, further comprising: a
comparing unit comparing the signal strength or correlation value,
which is measured by said measuring unit, with a predetermined
threshold value, and wherein said synchronization establishing unit
attempts to establish synchronization based the comparison of said
comparing unit.
4. The mobile station according to claim 1, wherein said
synchronization establishing unit selects for establishing
synchronization a carrier frequency having the spread signal whose
signal strength measured by said measuring unit is the
strongest.
5. The mobile station according to claim 1, wherein said
synchronization establishing unit sequentially attempts to
establish synchronization for the spread signal on the particular
channel in each carrier frequency in descending order of the signal
strength measured by said measuring unit.
6. The mobile station according to claim 1, wherein: said receiving
unit orthogonally demodulates a reception spread signal over a
single carrier frequency among the plurality of carrier
frequencies; said measuring unit generates timing-correlational
square amplitude calculation value data by calculating square
amplitude calculation values of correlation values measured for the
orthogonally demodulated spread signal; and a comparing unit
compares the correlational square amplitude calculation value with
a predetermined threshold value.
7. The mobile station according to claim 6, wherein said storing
unit stores only timing-correlational square amplitude calculation
value data exceeding the threshold value based on a result of a
comparison made by said comparing unit.
8. The mobile station according to claim 6, further comprising a
selecting unit for selecting timing-correlational square amplitude
calculation data having a maximum correlational square amplitude
calculation value from among timing-correlational square amplitude
calculation value data for each carrier frequency.
9. The mobile station according to claim 6, further comprising a
sorting unit for rearranging timing-correlation square amplitude
calculation value data of all of carrier frequencies, which are
generated by said measuring unit, in descending order of
correlational square amplitude calculation values.
10. The mobile station according to claim 6, further comprising: a
classifying unit for performing classification for a plurality of
pieces of timing-correlational square amplitude calculation value
data by recognizing the data to be transmitted from a same base
station, if the plurality of timing-correlational square amplitude
calculation value data indicating identical timing exist for each
carrier frequency; and a selecting unit for selecting only data
having a largest square amplitude calculation value from among
timing and square amplitude calculation value data corresponding to
spread signals of each base station, which are classified by said
classifying unit, wherein said synchronization establishing unit
uses only data selected by said selecting unit so as to establish
synchronization.
11. The mobile station according to claim 10, further comprising a
sorting unit for rearranging timing-correlational square amplitude
calculation value data of all of carrier frequencies, which are
generated by said measuring unit, in descending order of
correlational square amplitude calculation values, wherein said
classifying unit performs the classification based on a sorting
result of said sorting unit.
12. The mobile station according to claim 10, wherein reception
timing of the spread signal on the particular channel, which is
transmitted over the plurality of carrier frequencies, is shifted
by predetermined timing, the mobile station further comprising: a
delaying unit for delaying an output from said measuring unit by
the predetermined timing for each frequency; a controlling unit for
controlling said delaying unit, and for making said storing unit
store timing-correlational square calculation value data where the
reception timing of the spread signal on the particular channel,
which is transmitted over the plurality of carrier frequencies, is
cancelled; and a determining unit for determining that signals are
transmitted from a same base station if timing-correlational square
calculation value data stored in said storing unit indicate
identical timing.
13. A mobile station for use in a spread communication system
having a particular channel for establishing synchronization, the
particular channel for establishing synchronization existing on a
plurality of carrier frequencies, comprising: a receiving unit
receiving the plurality of carrier frequencies; a measuring unit
measuring a strength or a correlation value of a spread signal on
the particular channel for each of the plurality of carrier
frequencies; and a controller selecting a carrier frequency of the
plurality of carrier frequencies for performing a cell search based
on the measuring from the measuring unit.
14. The mobile station according to claim 13, wherein said
controller selects the carrier frequency for establishing
synchronization based on a carrier frequency having the spread
signal whose signal strength measured by said measuring unit is the
strongest.
15. The mobile station according to claim 13, further comprising: a
storing unit storing information about the spread signal of the
particular channel having the signal strength or correlation value
which is largest in each carrier frequency of the plurality of
carrier frequencies.
16. A mobile station for use in a spread communication system
having a particular channel for establishing synchronization, the
particular channel for establishing synchronization existing on a
plurality of carrier frequencies, comprising: a receiving unit
receiving the plurality of carrier frequencies; a measuring unit
measuring a strength or a correlation value of a spread signal on
the particular channel for each of the plurality of carrier
frequencies; and a controller determining the spread signal of the
particular channel having the signal strength or correlation value
which is largest in each carrier frequency of the plurality of
carrier frequencies, and selecting a carrier frequency for
performing a cell search.
17. A mobile station for use in a spread communication system
having a particular channel for establishing synchronization, the
particular channel for establishing synchronization existing on a
plurality of carrier frequencies, comprising: a receiving unit
receiving the plurality of carrier frequencies; a measuring unit
measuring a strength or a correlation value of a spread signal on
the particular channel for each of the plurality of carrier
frequencies; a selecting unit for selecting timing-correlational
square amplitude calculation data having a maximum correlational
square amplitude calculation value from among timing-correlational
square amplitude calculation value data for each carrier frequency;
and a controller selecting a carrier frequency of the plurality of
carrier frequencies for performing a cell search based on the
selecting unit.
18. A method for a spread communication system having a particular
channel for establishing synchronization, the particular channel
for establishing synchronization existing on a plurality of carrier
frequencies, the plurality of carrier frequencies transmitted from
one or more base stations, comprising the steps of: receiving the
plurality of carrier frequencies; measuring a strength or a
correlation value of a spread signal on the particular channel for
each of the plurality of carrier frequencies; and selecting a
carrier frequency of the plurality of carrier frequencies for
performing a cell search based on the measuring step.
19. The method according to claim 18, wherein the selecting step
selects the carrier frequency for establishing synchronization
based on a carrier frequency having the spread signal whose
measured signal strength is the strongest.
20. The method according to claim 18, further comprising the step
of: storing information about the spread signal of the particular
channel having the signal strength or correlation value which is
largest in each carrier frequency of the plurality of
frequencies.
21. A method for use in a spread communication system having a
particular channel for establishing synchronization, the particular
channel existing on a plurality of carrier frequencies, the
plurality of carrier frequencies transmitted from one or more base
stations, comprising the steps of: receiving the plurality of
carrier frequencies; measuring a strength or a correlation value of
a spread signal on the particular channel for each of the plurality
of carrier frequencies; determining the spread signal of the
particular channel having the signal strength or correlation value
which is largest in each carrier frequency of the plurality of
carrier frequencies; and selecting a carrier frequency for
performing a cell search based on the determining step.
22. A method for use in a spread communication system having a
particular channel for establishing synchronization, the particular
channel for establishing synchronization existing on a plurality of
carrier frequencies, the plurality of carrier frequencies
transmitted from one or more base stations, comprising the steps
of: receiving the plurality of carrier frequencies; measuring a
strength or a correlation value of a spread signal on the
particular channel for each of the plurality of carrier
frequencies; selecting timing-correlational square amplitude
calculation data having a maximum correlational square amplitude
calculation value from among timing-correlational square amplitude
calculation value data for each carrier frequency; and selecting a
carrier frequency for performing a cell search based on the
selecting timing-correlational square amplitude calculation data
step.
23. A spread communication system having a particular channel for
establishing synchronization, the particular channel for
establishing synchronization existing on a plurality of carrier
frequencies, comprising: a base station transmitting the particular
channel for establishing synchronization on one or more carrier
frequencies of the plurality of carrier frequencies; a receiving
unit receiving the plurality of carrier frequencies; a measuring
unit measuring a strength or a correlation value of a spread signal
on the particular channel for each of the plurality of carrier
frequencies; and a controller determining the spread signal of the
particular channel having the signal strength or correlation value
which is largest in each carrier frequency of the plurality of
carrier frequencies, and selecting a carrier frequency for
performing a cell search.
24. A mobile station for use in a spread communication system
having a particular channel for establishing synchronization, the
particular channel for establishing synchronization existing on a
plurality of carrier frequencies, comprising: a receiving unit
receiving the plurality of carrier frequencies; a measuring unit
measuring a strength of a spread signal on the particular channel
for each of the plurality of carrier frequencies; and a controller
selecting a carrier frequency of the plurality of carrier
frequencies for performing a cell search based on the measuring
from the measuring unit.
25. A method for a spread communication system having a particular
channel for establishing synchronization, the particular channel
for establishing synchronization existing on a plurality of carrier
frequencies, the plurality of carrier frequencies transmitted from
one or more base stations, comprising the steps of: receiving the
plurality of carrier frequencies; measuring a strength of a spread
signal on the particular channel for each of the plurality of
carrier frequencies; and selecting a carrier frequency of the
plurality of carrier frequencies for performing a cell search based
on the measuring step.
26. A cell search method in a spread communication system having a
particular channel for establishing synchronization existing on a
plurality of carrier frequencies, the plurality of carrier
frequencies transmitted from one or more base stations, comprising:
receiving the plurality of carrier frequencies; measuring a
strength or a correlation value of a spread signal on the
particular channel for each of the plurality of carrier
frequencies; determining the spread signal of the particular
channel having the signal strength or correlation value which is
largest in each carrier frequency of the plurality of carrier
frequencies; and performing a cell search in each carrier frequency
until a cell having the signal strength or correlation value
meeting a predetermined criteria is obtained.
27. A cell search method for use in a spread communication system
having a particular channel for establishing synchronization, the
particular channel for establishing synchronization existing on a
plurality of carrier frequencies, a carrier frequency including
multiple channels which are spread modulated with a spread code
which differs depending on each channel accommodated by a base
station, comprising the steps of: receiving the plurality of
carrier frequencies; measuring a strength or a correlation value of
a spread signal on the particular channel for each of the plurality
of carrier frequencies; determining the spread signal of the
particular channel having the signal strength or correlation value
which is largest in each carrier frequency of the plurality of
carrier frequencies; and performing a cell search in each carrier
frequency until a cell having the signal strength or correlation
value meeting a predetermined criteria is obtained.
28. A mobile station for use in a spread communication system
having a base station transmitting a particular channel for
establishing synchronization on one or more carrier frequencies, a
carrier frequency including multiple channels which are spread
modulated with a spread code which differs depending on each
channel accommodated by the base station, comprising: a receiving
unit receiving the plurality of carrier frequencies; a measuring
unit measuring a strength or a correlation value of a spread signal
on the particular channel for each of the plurality of carrier
frequencies; and a controller determining the spread signal of the
particular channel having the signal strength or correlation value
which is largest in each carrier frequency of the plurality of
carrier frequencies, and performing a cell search in each carrier
frequency until a cell having the signal strength or correlation
value meeting a predetermined criteria is obtained.
29. A cell search method for a mobile station in a spread
communication system having a base station transmitting a
particular channel for establishing synchronization on one or more
carrier frequencies, a carrier frequency including multiple
channels which are spread modulated with a spread code which
differs depending on each channel accommodated by the base station,
comprising: measuring a strength or a correlation value of a spread
signal on the particular channel for each received carrier
frequency of the plurality of carrier frequencies; and determining
the spread signal of the particular channel having the signal
strength or correlation value which is largest in each carrier
frequency of the plurality of carrier frequencies; and performing a
cell search for establishing synchronization in each carrier
frequency until a cell having the signal strength or correlation
value meeting a predetermined criteria is obtained.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DS-CDMA (Direct Sequence-Code
Division Multiple Access) base station asynchronous cellular
system, and more particularly to an initial cell search method for
a mobile station and a transmission power control method for a
perch channel at a base station, which is combined with the initial
cell search method.
2. Description of the Related Art
In recent years, the downsizing and the popularization of a
cellular phone, etc. have been rapidly advancing with the
size-reduction of a processor, etc. In a system accommodating such
a cellular phone, a continuously moving mobile station must be
accommodated in a suitable base station. At the same time, a system
which accommodates mobile stations as many as possible is desired
for the upcoming popularization of a cellular phone. However, since
an available frequency bandwidth is limited with a conventional
frequency division multiplexing technique, the number of mobile
stations which can be accommodated is limited as a matter of
course. Accordingly, close attentions are currently paid to a CDMA
communication using a direct sequence. In the CDMA communication, a
transmission signal is spread-modulated with a spread code which
differs depending on each channel accommodated by a base station.
On a receiving side, the transmission signal is regenerated by
despreading the spread-modulated signal with the same code as that
used by the base station. In this case, the reception signal must
be multiplied by the despread code (the same as that used on the
transmitting side) at suitable timing on the mobile station side,
that is, the receiving side. Accordingly, to which channel of which
base station a mobile station is to be connected is determined in
the initial stage of the communication. At the same time, the
multiplication timing of a despread code, which is intended to
continuously connect the mobile station to that channel must be
obtained. Namely, an initial cell search must be made.
The initial cell search is an operation for initially determining a
visited cell of a mobile station (the visited cell is an area where
a particular base station can accommodate a mobile station when the
mobile station stays within the visited cell) when the mobile
station power is turned on. At this time, the mobile station
receives a perch channel transmitted from the base station, and
attempts to obtain the information broadcast by the channel. The
perch channel is a channel which helps a mobile station identify
the despread code of the signal transmitted from a base station, or
capture the channel transmitted to obtain despreading timing in the
initial cell search.
In the system which is assumed by the present invention and will be
described later, a perch channel is spread with a short code for
synchronously capturing the perch channel, and a long code for
identifying the channel from the base station. The perch channel is
assumed to be further spread with a group short code indicating to
which group the long code used for the perch channel belongs among
many long codes so as to facilitate a long code search. Here, all
of the short code, the group short code, and the long code are
spread codes which respectively have their use purposes.
Since which long code is used for a certain downstream channel (a
channel used for a communication from a base station to a mobile
station) cannot be identified, it must be identified by examining
the long code of a particular (perch) channel. Additionally, also
the phase of the long code (the despreading timing when the long
code is used in a communication) must be identified.
As the conventional initial cell search method of a DS-CDMA system
with a control channel, which uses a long code which differs
depending on each cell and a synchronization short code common to
all cells, the technique disclosed by the Japanese Laid-open Patent
Publication No. 10-126380 can be cited. With this conventional
technique, the initial cell search for a single-frequency carrier
wave signal can be made at high speed. Furthermore, as the
technique obtained by further developing the above described
conventional technique, "A High-speed Cell Search Method Using a
Long Code Mask in DS-CDMA Base Station Asynchronous Cellular"
recited in the Electronic Information Communication Society
Research and Technical Report RCS96-i22) exists. The format of the
perch channel signal to which the above described techniques are
applied is shown in FIG. 1.
FIG. 1 shows that a perch channel 100 signal is transmitted from
the left to the right of this figure. A long code is intended to
identify a channel accommodated by a base station. When a
communication is made using the channel identified by the long code
used by a certain base station, signals are transmitted and
received by spreading and despreading the signals with this long
code in all cases during a call. The perch channel signal is spread
with the long code unique to the channel, and is further spread
with a short code for synchronously capturing the perch channel 100
signal, which is common to all of base stations. The beginning
portion of the long code, which is spread with the common short
code, does not include a long code. The portion where no long code
exists is further spread with a group short code indicating to
which group the used long code belongs among many long code groups
in addition to the common short code.
This initial cell search method is mainly composed of three stages.
These stages are summarized below.
[First Stage] A destination base station whose reception power is
maximized is determined by performing a correlational square
amplitude operation between a reception signal and a short code,
and by taking an average value of the correlational square
amplitude operation. At the same time, slot synchronization is
made. Here, the slot synchronization is the timing at which a
despreading process is performed with the short code, the group
short code, and the long code. Additionally, the correlational
square amplitude calculation is an operation for calculating the
correlation values for an I signal and a Q signal of a reception
signal, and for squaring and adding the correlation values for the
I signal and the Q signal, which are obtained by the above
described calculation. This operation is equivalent to an operation
for squaring the length of a vector when the correlation value of a
signal is recognized to be the vector on an I-Q plane where the
correlation values of the I and the Q signal are respectively
indicated by the horizontal and the vertical axes. The reason that
the average value of the correlational square amplitude calculation
is taken is to suppress an influence of noise included in a
correlation value. [Second Stage] A group short code corresponding
to a plurality of long codes is identified by using the slot
synchronization timing established in the first stage. Used to
identify the group short code is a method for calculating the
correlation value of a reception signal with the group short code,
and for determining whether or not the correlation value equal to
or larger than a predetermined value is obtained. Long code
candidates are limited at this stage. [Third Stage] The long code
synchronization and the long code of the perch channel are
determined based on the result of the correlational square
amplitude operation between the reception signal and the long code.
The long code determination method is a method for calculating a
correlation value with a reception signal by using both of the long
code and the common short code, and for determining that the long
code used for the perch channel is obtained when a predetermined or
larger correlation value is obtained. If this process is
unsuccessfully performed, the process goes back to the first stage
and another long code candidate is used.
For the details of the conventional initial cell search method,
please refer to the above described patent publication or technical
document.
However, it is impossible to apply this technique to a DS-CDMA
cellular system using a perch channel of a
multiple-carrier-frequencies signal as it is. This is because perch
channels exist at a plurality of frequencies, and the operation for
receiving all of the frequencies is essential for the initial cell
search in such a system. A solution to this problem is not recited
by the conventional technique. If the above described conventional
initial search method is sequentially performed for the respective
carrier frequencies, in the worst case, the operations at the first
through the third stages may be considered to be performed for all
of the frequencies. In this case, at least a cell search time
multiplied by the number "Nf" (the number of downstream carrier
frequencies) of carrier frequencies is required compared with the
case of a single carrier frequency.
Additionally, when many mobile stations concentrate on a single
cell in the conventional DS-CDMA system, mobile stations exceeding
the capacity of one base station attempt to access the station,
which can possibly lead to a fault such as a communication quality
degradation or communication disability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a system which can
efficiently accommodate subscribers in respective base stations in
a spread communication system using a single-carrier frequency or
multiple carrier frequencies.
A mobile station according to the present invention, which is a
mobile station for use in a spread communication system having a
particular channel for establishing synchronization, comprises: a
receiving unit for receiving a spread signal of a particular
channel; a measuring unit for measuring the strength or correlation
value of the spread signal received by the receiving unit; a
comparing unit for comparing the signal strength or correlation
value, which is measured by the measuring unit, with a
predetermined threshold value; a storing unit for storing the
information about the particular channel having the signal strength
or correlation value, which is larger than the predetermined
threshold value; and a synchronization establishing unit for
establishing synchronization based on the information stored in the
storing unit.
A base station according to the present invention, which is a base
station for use in a spread communication system having a
particular channel for establishing synchronization, comprises: at
least one transmitting unit for transmitting a spread signal on the
particular channel over at least one carrier frequency by varying a
transmission power; a measuring unit for measuring the number of
mobile stations accommodated in the local station or the
transmission qualities of the reception signals from the mobile
stations; and a controlling unit for controlling the number of
mobile stations accommodated in at least one frequency by variably
controlling the transmission power of the spread signal on the
particular channel, which is accommodated in at least one
frequency.
A system according to the present invention, which is a spread
communication system having a particular channel for establishing
synchronization, comprises: a base station having a capability for
controlling the transmission power level of the spread signal
portion for establishing synchronization on the particular channel;
and a mobile station having a capability for selecting a base
station to be accessed according to the transmission power level of
the received spread signal portion for establishing synchronization
on the particular channel.
According to the present invention, even if a communication service
using a plurality of frequencies is provided, a mobile station can
select a channel at a suitable frequency, and access a base station
in a spread communication system.
Additionally, the base station can control the frequency which the
mobile station subscribes by variably controlling the transmission
power of a spread signal when transmitting the spread signal on a
particular channel for establishing synchronization, and can
suitably allocate mobile stations to a plurality of frequencies.
Furthermore, a certain base station increases the transmission
power more than that in a different base station, so that a mobile
station accessing the different base station can be accommodated by
the certain base station. As a result, mobile stations can be
suitably distributed and allocated to respective base stations
without imposing a heavy load on only one base station.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows one example of the format of a perch channel signal in
a conventional CDMA cellular system;
FIG. 2 is a block diagram showing the configuration of a mobile
station according to a first preferred embodiment of the present
invention;
FIG. 3 shows one example of a rectifying circuit shown in FIG.
1;
FIG. 4 is a block diagram showing the configuration of a mobile
station according to a second preferred embodiment of the present
invention;
FIG. 5 is a block diagram showing the configuration of a mobile
station according to a third preferred embodiment of the present
invention;
FIG. 6 exemplifies the configuration of a square amplitude
calculating circuit;
FIG. 7 exemplifies the format of data stored in a storing circuit 6
shown in FIG. 4;
FIG. 8 is a block diagram showing the configuration of a mobile
station according to a fourth preferred embodiment of the present
invention;
FIG. 9 is a block diagram showing the configuration of a mobile
station according to a fifth preferred embodiment of the present
invention;
FIG. 10 is a block diagram showing the configuration of the mobile
station according to a sixth preferred embodiment;
FIG. 11 shows a mobile station according to a seventh preferred
embodiment of the present invention (No. 1);
FIG. 12 shows the mobile station according to the seventh preferred
embodiment of the present invention (No. 2);
FIG. 13 shows the mobile station according to the seventh preferred
embodiment (No. 3);
FIG. 14 shows a mobile station according to an eighth preferred
embodiment of the present invention;
FIG. 15 shows a base station according to a first preferred
embodiment of the present invention;
FIG. 16 shows a base station according to a second preferred
embodiment of the present invention;
FIG. 17 shows a base station according to a third preferred
embodiment of the present invention; and
FIG. 18 shows a base station according to a fourth preferred
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2 is a block diagram showing the configuration of a mobile
station according to a first preferred embodiment of the present
invention.
In this preferred embodiment, the presence/absence of a carrier
wave is initially determined for all of carrier frequencies. Then,
whether or not an available perch channel exists is determined in
each of the carrier frequencies by measuring the strength of a
reception signal at each of the carrier frequencies, and by
comparing the measured strength with a predetermined threshold
value. If an available perch channel is determined to exist only in
some of the carrier frequencies at this state, the time taken to
despread the frequencies where no necessary signal exists can be
saved by making a cell search for those carrier frequencies.
The signal received by an antenna 7 is input to a receiving circuit
1. The receiving circuit 1 includes a frequency converting circuit
and a local oscillator, which are not shown in this figure. The
frequency converting circuit converts the cyclic signal output from
the local oscillator into the frequency specified by an externally
input digital signal, so that the locally oscillated signal that
the receiving circuit 1 requires to receive a signal can be varied.
The receiving circuit 1 is intended to convert the signal received
by the antenna 7, for example, into a baseband signal, and to
output the baseband signal. The signal received by the receiving
circuit 1 is an analog signal, and is input to a rectifying circuit
2. The rectifying circuit 2 includes a switch. The rectifying
circuit 2 turns off the switch in a cyclic time period during which
perch channel signals arrive, and turns on the switch at the end of
the cyclic time period to emit the electric charge of the input
analog signals, which is accumulated in an internally arranged
capacitor. Namely, the analog signals which are received by the
antenna 7 and output from the receiving circuit 1 are integrated by
the rectifying circuit 2. The average value of the signals received
during the perch channel signal cyclic time period can be obtained
if the integrated value output from the rectifying circuit 2 is
divided by the time (the cyclic time period) taken to integrate the
signals. However, the integrated value itself is used to simplify
the circuit configuration here. The integrated value output from
the rectifying circuit 2 is A/D-converted by an A/D converter 3.
The digital signal obtained by the A/D conversion is compared with
a predetermined threshold value by a comparing circuit 4. The
output of the comparing circuit 4 becomes "1" when a digital signal
exceeding the threshold value is obtained. The signal indicating
the value "1" is input to a storing circuit 6 as a Write
(Write-enable) signal, so that the frequency data input to the
receiving circuit 1 at this time is stored in the storing circuit
6. This frequency data is provided to the storing circuit 6 as an
Nbf-bit signal from a controlling circuit 5.
The controlling circuit 5 stores the frequencies of a plurality of
perch channels beforehand, and specifies the frequency of the perch
channel to be frequency-detected for the receiving circuit 1 with
frequency specification data. The receiving circuit 1 receives the
perch channel signal having the frequency specified by the
controlling circuit 5. The receiving circuit 1 converts the signal
having the specified frequency, for example, into a baseband
signal, and outputs the baseband signal to the rectifying circuit
2. The rectifying circuit 2 integrates the signals input from the
receiving circuit 1 during the perch channel signal cyclic time
period by turning on/off the internal switch with the signal
(switching signal) instructing the cyclic time period timing. As
described above, the output of the rectifying circuit 2 is
A/D-converted by the A/D converter 3, and is input to the comparing
circuit 4 as an Nad-bit digital signal in order to be compared with
a threshold value. If the numeric value represented by the Nad bits
is larger than the threshold value as a result of the comparison, a
Write signal is applied to the storing circuit 6, so that the
Nbf-bit frequency specification data input from the controlling
circuit 5 is stored.
The controlling circuit 5 applies a Read signal to the storing
circuit 6, reads the Nbf-bit frequency data candidate from the
storing circuit 6, sets the read data in the receiving circuit 1,
and makes a cell search.
All of the outputs of the controlling circuit 5 and the frequency
specification data may be stored in the storing circuit 6 without
making the above described comparison with the threshold value.
Additionally, the output of the rectifying circuit 2 is compared
with the threshold value of an analog voltage by an analog
comparator, so that the result of the comparison may be used as a
Write signal to the storing circuit. Furthermore, the output of the
A/D converter 3 is compared with a threshold value by a CPU, etc.,
so that a frequency candidate data may be selected.
Note that the configuration for making a cell search is not shown
in FIG. 2 although the controlling circuit 5 obtains frequency
candidate data for making a cell search. Because a conventional
method can be used as the cell search method and a known technique
can be also used as the hardware configuration, a cell search
configuration is not particularly shown. Accordingly, the cell
search method and the hardware configuration implementing this
method are not particularly referred to in the explanations to be
provided about the preferred embodiments.
FIG. 3 shows one example of the rectifying circuit shown in FIG.
2.
This rectifying circuit is implemented by adding a switch 10 to a
general bridge-type full-wave rectifying circuit 9. The signal
input from an input terminal 8 is rectified by a bridge 9a and a
capacitor 9b. Particularly, in this preferred embodiment, the
switch 10 is arranged and turned off during the perch channel
signal cyclic time period. The electric charge of the rectified
signal is accumulating in the capacitor 9b during this time period.
The operation for accumulating the electric charge of a rectified
signal in the capacitor 9b corresponds to the above described
signal integration. The rectifying circuit may be configured by
using a half-wave rectifying circuit although FIG. 3 exemplifies
the configuration using the full-wave rectifying circuit.
FIG. 4 is a block diagram showing the configuration of a mobile
station according to a second preferred embodiment of the present
invention.
In this figure, the same constituent elements as those shown in
FIG. 2 are denoted by the same reference numerals.
According to this preferred embodiment, if a signal available for a
plurality of carrier frequencies is determined to exist, a cell
search is made for the frequency at which the strength of the
signal becomes a maximum among the carrier frequencies where the
signal exists. After the above described process at the first stage
is terminated, the cell search for a single frequency is made in
descending order of the strength of the signal.
Namely, a receiving circuit 1 to which Nbf-bit frequency
specification data is input from a controlling circuit 1 performs
frequency conversion for the signal having the frequency specified
by this input, and outputs the signal obtained by the conversion to
a rectifying circuit 2. The rectifying circuit 2 rectifies the
input signal from the receiving circuit 1 based on the switching
signal input from the controlling circuit 5, and integrates the
signal obtained by the rectification during a perch channel signal
cyclic time period. The result of the integration is input to an
A/D converter 3. After the signal is converted into a digital
signal, it is input as an Nad-bit digital signal to a comparing
circuit 4 and also to a storing circuit 6. If the integrated value
of the rectifying circuit 2 is larger than a threshold value as a
result of the comparison made by the comparing circuit 4, a Write
signal is input from the comparing circuit 4 to the storing circuit
6. The Nbf-bit frequency specification data output from the
controlling circuit 5 and the Nad-bit signal value obtained by
digitizing the integrated value of the rectifying circuit 2 are
corresponded and stored in the storing circuit 6.
The controlling circuit 5 shown in FIG. 4 reads the frequency data
corresponding to the maximum integrated value data from the storing
circuit 6, and makes a conventional cell search for a single
frequency. In this case, the controlling circuit 5 references the
integrated value data stored in the storing circuit 6, searches for
the maximum integrated value data, and obtains the frequency
specification data stored in correspondence with the maximum
integrated value data. Then, the controlling circuit 5 makes the
conventional cell search for a single frequency for the frequency
specified by this frequency specification data. Additionally, in
the configuration shown in FIG. 4, a method for obtaining a
predetermined number of pieces of frequency specification data from
the storing circuit 6 in descending order of an integrated value,
and for individually making the conventional cell search for a
single frequency for the plurality of frequency specification data,
may be used other than the method for using the maximum frequency
data as a cell search target. By selecting a predetermined number
of frequencies in descending order of an integrated value as
described above, processing time can be significantly reduced
compared with the case where a cell search is made for all of
stored frequencies. Explanation about the conventional cell search
method for a single frequency is omitted here.
FIG. 5 is a block diagram showing the configuration of a mobile
station according to a third preferred embodiment of the present
invention.
According to this preferred embodiment, after the
timing-correlational square amplitude calculation between the
output of the receiving circuit 21 and a common short code is made,
and a cell search is made based on this data. Here, the
timing-correlational square amplitude calculation means the
acquisition of correlation values obtained by matched filters, and
the information about the timing at which a common short code and a
demodulation signal are multiplied.
A receiving circuit 21 includes a frequency converting circuit (not
shown), and can set a locally oscillated frequency with externally
input data by using the frequency converting circuit. The receiving
circuit 21 generates the signal having the corresponding frequency
based on the frequency specification data provided by a controlling
unit 27, and converts the frequency of the signal received by an
antenna 20 by using this locally oscillated signal. For example, an
RF band signal received by the antenna 20 is converted into an IF
band signal. Then, the signal whose frequency is converted by the
receiving circuit 21 is input to an orthogonal demodulator 22,
where the signal is demodulated into an I and Q signals being
orthogonal signals. Then, the I and Q signals are respectively
converted into digital signals by A/D converters 23-1 and 23-2, and
input to matched filters 24-1 and 24-2. The common short code of
the perch channel signal to be cell-searched is input to the
matched filters 24-1 and 24-2, which respectively calculate and
output the correlation values between the common short code and the
converted digital I and Q signals. A square amplitude calculating
circuit 25 is a circuit which calculates the square of the distance
from the coordinate origin of the complex number value on a complex
plane, by recognizing the correlation values output from the
matched filters 24-1 and 24-2 to be the real and imaginary number
parts of a complex number (for example, respectively recognizes the
correlation values between the common short code and the I signal
and between the common short code and the Q signal to be a real and
imaginary number parts), and outputs the calculated value. The
output of the square amplitude calculating circuit 25 is stored in
the storing circuit 26 as a correlational power value along with
the frequency specification data output from the controlling unit
27. The controlling unit 27 reads the stored data from the storing
circuit 26 by providing a Read signal to the storing circuit 26,
and selects a frequency and timing candidates from the stored data.
A correlation value is stored in the storing circuit 26 each time
the matched filters 24-1 and 24-2 multiply a common short code at a
different timing. Therefore, the timing candidate can be determined
based on a memory location in the storing circuit 26 according to
the correspondence between frequency and timing.
FIG. 6 exemplifies the configuration of the square amplitude
calculating circuit 25.
When the correlation values are obtained respectively for the I and
Q signals which are orthogonally demodulated by the orthogonal
demodulator 22, the correlation values are respectively input to
multipliers 28-1 and 28-2 as inputs 1 and 2. The inputs 1 and 2 are
branched and respectively input to the multipliers 28-1 and 28-2.
Then, the inputs 1 and 2 are respectively squared by the
multipliers 28-1 and 28-2, and input to an adder 29, which adds
these values. As a result, a correlation power value
I.sup.2+Q.sup.2 is output from the adder 29 based on the assumption
that the values of the inputs 1 and 2 are respectively represented
as I and Q.
FIG. 7 exemplifies the storage format of the data stored in the
storing circuit 26 shown in FIG. 5.
In the storing circuit 26 shown in FIG. 5, data items such as a
correlational power value, a timing candidate, and a frequency
candidate are stored. The format shown in FIG. 7 exists as the
storage format for efficiently storing these data items from an
access or capacity viewpoint. In this figure, a correlational power
value is stored in each cell 71 in a two-dimensional table 70. Each
column in the table 70 corresponds to each specification frequency
"f", while each row in the table 70 corresponds to each timing
candidate "t". The timing candidate "t" is the timing at which a
common short code is multiplied by a demodulation signal. Normally,
when a spread code is provided, a matched filter sequentially
outputs a correlation value while shifting the multiplication
timing of a spread code in synchronization with the clock of a
receiving device. Accordingly, the multiplication timing of a
spread code, that is, a timing candidate, can be identified at the
timing of the clock within a receiving device by storing in which
order a correlation value is output.
Therefore, a correlational power value is stored in the cell at the
intersection point of the multiplication timing (timing candidate)
when the correlational power value is obtained and a specification
frequency. By arranging the storing circuit 26 as the table 70,
only correlational power values may be stored therein. Furthermore,
a column and row addresses respectively become frequency
specification data (a frequency candidate) and multiplication
timing (a timing candidate) when a correlation power value is
written/read to/from the storing circuit 26.
FIG. 8 is a block diagram showing the configuration of a mobile
station according to a fourth preferred embodiment of the present
invention.
In this figure, the same constituent elements as those shown in
FIG. 5 are denoted by the same reference numerals.
The signal received by an antenna 20 is frequency-modulated to an
IF band signal by a receiving circuit 21, and is input to an
orthogonal demodulator 22. The orthogonal demodulator 22
demodulates the signal from the receiving circuit 21 into an I and
Q signals, and respectively inputs them to A/D converters 23-1 and
23-2. The I and Q signals which are converted into digital signals
are respectively input to matched filters 24-1 and 24-2, which
respectively calculate the correlation values between the common
short code and the I and Q signals. The correlation values of the I
and Q signals which are respectively output from the matched
filters 24-1 and 24-2 are input to a square amplitude calculating
circuit 25. The square amplitude calculating circuit 25 calculates
and outputs the total (correlational power value) of the squares of
the correlation values between the common short code and the I and
Q signals. The output of the square amplitude calculating circuit
25 is input to a storing circuit 26 and also to a comparing circuit
30. The comparing circuit 30 compares the output (correlational
power value) of the square amplitude calculating circuit 25 with a
predetermined threshold value. If the output of the square
amplitude calculating circuit 25 is larger than the threshold value
as a result of the comparison between the output of the square
amplitude calculating circuit 25 and the threshold value, the
output (determination information) of the comparing circuit 30
becomes "1". The value "1" is input to the storing circuit 26 as a
Write signal, so that only the frequency specification data
corresponding to the correlational power value exceeding the
threshold value and the correlation power value are stored in the
storing circuit 26.
Then, a controlling unit 27 reads the correlational power value and
the frequency candidate (frequency specification data)
corresponding thereto from the storing circuit 26, selects the
timing corresponding to the correlational power value
(correlational square amplitude calculation value), which becomes a
maximum at each frequency, and makes a conventional cell search for
a single frequency for the frequency candidate corresponding to
this timing. Or, the controlling unit 27 may make a cell search by
selecting the frequency of the maximum correlational square
amplitude calculation value among all of the frequencies stored in
the storing circuit 26 and its corresponding timing. The slot
timing (the timing at which a common short code and a demodulation
signal are multiplied), which corresponds to a correlational power
value, can be known from the relationship between the operations of
the matched filters 24-1 and 24-2 and the clock within the device
by detecting in which order the correlation value is read out among
the correlation values which are sequentially output from the
matched filters 24-1 and 24-2.
According to this preferred embodiment, a threshold value
determination is made, and the data about the frequency of a perch
channel signal, which is considered to be valid, is stored in the
storing circuit 26, so that the capacity of the storing circuit 26
and the operation amount of subsequent data processing (maximum
value selection and sorting) can be reduced.
FIG. 9 is a block diagram showing the configuration of a mobile
station according to a fifth preferred embodiment of the present
invention.
In this figure, the same constituent elements as those shown in
FIG. 5 are denoted by the same reference numerals.
According to this preferred embodiment, the timing corresponding to
the data of the maximum square amplitude calculation value is
determined for each frequency among the data stored in a storing
circuit 26. A maximum value determining circuit 31 may be
implemented by software with a CPU. Additionally, the maximum value
determining circuit 31 may select the timing corresponding to the
maximum square amplitude calculation value at all of frequencies.
Furthermore, the maximum value determining circuit 31 may calculate
the data stored in the storing circuit 26 during a plurality of
common short code cyclic time periods, obtain the averaged data in
these cyclic time periods, and determine the maximum value among
the averaged data.
The signal received by an antenna 20 is frequency-modulated to an
IF band signal, and is demodulated by an orthogonal demodulator 22.
After the demodulated I and Q signals are respectively converted by
A/D converters 23-1 and 23-2, the correlation values between a
common short code and the I and the Q signals are respectively
calculated by matched filters 24-1 and 24-2. Then, the square
amplitude calculation value (correlational power value) of the
correlation values of the I and Q signals is obtained by a square
amplitude calculating circuit 25, and the obtained value is stored
in the storing circuit 26. In this preferred embodiment, a maximum
value determining circuit 31 reads the frequency specification data
and the correlational power value, which are stored in the storing
circuit 26, independently from a controlling unit 27, and
determines the frequency specification data (frequency candidate)
corresponding to the maximum correlational power value. As the way
of determining the correlational power value at this time, several
methods exist as described above.
When the frequency candidate corresponding to the maximum
correlational power value is determined by the maximum value
determining circuit 31, the controlling unit 27 obtains the
frequency candidate and the timing candidate, which correspond to
the maximum correlational power value, from the storing circuit 26
by applying a Read signal to the storing circuit 26, and makes a
cell search.
FIG. 10, is a block diagram showing the configuration of a mobile
station according to a sixth preferred embodiment of the present
invention.
In this figure, the same constituent elements as those shown in
FIG. 9 are denoted by the same reference numerals.
According to this preferred embodiment, a cell search is made
sequentially from the frequency and the timing, which correspond to
larger correlational square amplitude operation value data, among
the timing-correlational square amplitude calculation value data of
all of frequencies.
In this preferred embodiment, the above described cell search
capability may be implemented by software with a CPU having a
sorting circuit 32 which rearranges data such as frequency
candidates, timing candidates, etc., which are stored in a storing
circuit 26, in descending order of a square amplitude calculation
value. Additionally, data such as the frequencies, timing data,
etc. stored in the storing circuit 26 may be rearranged after
averaging the data during a plurality of common short code cyclic
time periods also in this preferred embodiment.
The signal received by an antenna 20 is frequency-modulated to an
IF band signal by a receiving circuit 21, and is demodulated by an
orthogonal demodulator 22. The demodulated I and Q signals are
respectively converted into digital signals by A/D converters 23-1
and 23-2, and the correlation values between a common short code
and the I and Q signals are respectively calculated by matched
filters 24-1 and 24-2. Then, the correlation values of the I and Q
signals are squared by a square amplitude calculating circuit 25,
and a correlational power value (correlational square amplitude
calculation value) of the I and Q signals is calculated. The
obtained value is stored in the storing circuit 26 along with its
corresponding frequency specification data. The sorting circuit 32
searches for the correlational power values stored in the storing
circuit 26, and rearranges the data within the storing circuit 26
in descending order of a correlational power values. Or, the
sorting circuit 32 first searches the frequency data within the
storing circuit 26, and rearranges the data having the same
frequency in descending order of a correlational power value in a
group of the data having the same frequency.
A controlling unit 27 obtains a frequency and timing candidates
sequentially from the data having a larger correlational power
value from the storing circuit 26 where the data are rearranged as
described above, and makes a cell search.
FIGS. 11 through 13 show a mobile station according to a seventh
preferred embodiment of the present invention.
Since signals in a plurality of carrier waves transmitted at the
same power from one base station have almost the same attenuation
characteristic, no difference is considered to be made whichever
signal is adopted. Therefore, only the signal having the maximum
correlational square amplitude calculation value is used for a
comparison.
FIG. 11 exemplifies the configuration of the mobile station
according to the seventh preferred embodiment.
In this figure, the same constituent elements as those shown in
FIG. 10 are denoted by the same reference numerals.
The mobile station according to this preferred embodiment comprises
a circuit for sorting the data of stored square amplitude
calculation values, and a circuit for estimatingly classifying the
data into respective base station data.
The sorting and the estimatingly-classifying capabilities are
implemented by software with a CPU 35. However, these capabilities
may be configured by hardware.
The signal received by an antennal 20 is frequency-modulated to an
IF band signal, and demodulated into an I and Q signals by an
orthogonal demodulator 22. After the demodulated I and Q signals
are respectively converted into digital signals by A/D converters
23-1 and 23-2, they are input to matched filters 24-1 and 24-2. The
correlation values between a common short code and the digital I
and Q signals are calculated by the matched filters 24-1 and 24-2,
and the calculation results are output to a square amplitude
calculating circuit 25. The square amplitude calculating circuit 25
respectively calculates the square amplitudes for the correlation
values of the I and Q signals, and calculates the correlational
power value of the I and Q signals. The calculated correlational
power value is transmitted to a CPU 35, which stores this value in
a storing circuit 36. At the same time, a process to be described
later is performed for this value. Additionally, the CPU 35
receives the frequency specification data corresponding to the
correlational power value stored in the storing circuit 36 from a
controlling unit 27, and stores this data in correspondence with
the correlational power value.
After the CPU 35 performs a predetermined process, it outputs a
frequency and timing candidates to the controlling unit 27 to make
the controlling unit 27 perform a cell search.
FIG. 12 is a flowchart exemplifying the estimating-classification
process executed by the CPU 35 shown in FIG. 11.
In this example, for the data having the same timing, only the data
having the maximum correlational square amplitude calculation value
is left and the remaining data is discarded. Note that this process
may be performed after stored data is averaged in a plurality of
common short code cyclic time periods.
FIG. 13 exemplifies the data arrangement in the storing circuit
36.
In the storing circuit 36, records, each of which is composed of
data items such as a ranking, frequency data, timing (phase), and a
correlational square amplitude calculation value, are stored in the
form of a table. Each data item is composed of 1 word, and each
record is composed of 4 words. Since one-word data is stored at one
address in the storing circuit 36, a read/write operation can be
made from/to each record in units of data items.
Here, the storage unit of each record is assumed to be referred to
as an entry in the storing circuit 36. Additionally, as shown in
FIG. 13, the entry address at which the first record of the storing
circuit 36 is stored is assumed to be "DataStart", while the entry
address at which the last record is stored is assumed to be
"DataEnd".
In such a configuration, "N" records with the rankings 1 through
"N" are stored in the respective entries addressed at "DataStart",
"DataStart+4", "DataStart+8", . . . , "DataEnd".
The estimatingly-classifying process executed by the CPU 35 is
explained by referring to FIGS. 12 and 13. Assume that records are
rearranged in descending order of a correlational square amplitude
calculation value as illustrated in FIG. 13 before the process
shown by the flowchart of FIG. 12 is executed. Also this process is
performed by the CPU 35. After the process of the flowchart shown
in FIG. 12 is performed, desired records are arranged in descending
order of a correlational square amplitude calculation value at
addresses "DataStart" to "DataEnd+3". Also this arrangement process
is performed by the CPU 35. As a matter of course, data arranged in
ascending order can be generated.
First, suppose that the records are stored in the storing circuit
36 in the form shown in FIG. 13.
In FIG. 12, the entry address "DataStart" of the first record with
the ranking 1, which is stored in the storing circuit 36, is
assigned to a variable "X", in step S1. Additionally, the entry
address of the next record with the ranking 2 among the records
shown in FIG. 13 is assigned to a variable "Y". In step S2, it is
determined whether or not the variable "X" is larger than a
variable "DataEnd", that is, whether or not the process is
performed for the records in all the entries. If the determination
results in "YES" in step S2, it means that the process is completed
for the records in all the entries. Therefore, the process is
terminated. If the determination results in "NO" in step S2, a
record to be processed is left. Therefore, the flow goes to step
S4, where it is determined whether or not the variable "Y" is
larger than the variable "DataEnd". This is intended to determine
that the variable "Y" indicating the entry address of the record to
be compared with the record having the entry address equal to the
variable "X" exceeds "DataEnd", that is, no record to be compared
is left in the storing circuit 36. If the determination in step S4
results in "YES", a record to be compared reaches the last entry.
Therefore, the variable "X" indicating the entry address of the
record at the comparison source is incremented by 4, and the value
of the variable "Y" is set to a value which is larger than the
updated value of the variable "X" by 4 (step S3). Control then
transfers to the next entry record, that is, the process of the
timing set in the record. If the determination results in "NO" in
step S4, the contents of the addresses (X+2) and (Y+2) are
respectively loaded into registers A and B. Each of the addresses
"X" and "Y" indicates the address at which the data item of the
ranking of each record is stored. The address of each entry, to
which "2" is added, indicates the address at which the data item of
the timing of each record is stored. Accordingly, timing data of
each record to be compared is loaded into the registers A and B. In
step S6, the value obtained by (register A-register B) is stored in
a register C. Then, it is determined whether or not the content of
the register C is "0" in step S7. That is, it is determined whether
or not the timing data of the two records are the same. This
determination is based on the following consideration. If signals
are transmitted from the same base station, their timing are
estimated to be the same even if their frequencies are different.
That is, the data at the same timing are those transmitted from the
base station. Therefore, it is sufficient to leave any one of the
data.
If the determination results in "NO" in step S7, the signals are
not the ones transmitted from the same base station. The flow
therefore goes to step S14 where the entry address of the record to
be compared is changed to the next entry address. The flow then
goes back to step S4, and the above described process is repeated.
If the determination results in "YES" in step S7, it means that the
timing data of the two records are the same. Accordingly, it is
judged that the signals are transmitted from the same base station,
and either of them may be left. The flow then goes to step S8 where
the contents at the addresses "X+3" and "Y+3" are respectively
loaded into the registers A and B. In step S9, the value obtained
by (register B-register A) is stored in the register C. In step
S10, it is determined whether or not the register C is larger than
"0". This is intended to determine which of the correlational
square amplitude calculation values of the records at the two entry
addresses "X" and "Y" is larger. Namely, this is based on the
consideration such that it is sufficient to store the signal of a
larger correlational square amplitude calculation value.
If the determination results in "NO" in step S10, the correlational
square amplitude calculation value of the record at the entry
address "X" at the comparison source is larger. Therefore, the
record at the comparison destination "Y" is changed. Namely, the
flow goes to step S14 where the value of the variable "Y" is
incremented by 4 in order to read the record in the succeeding
entry from the storing circuit 36 by setting Y=Y+4. The flow goes
back to step S4, and the above described process is repeated. If
the content of the register C is larger than "0" in step S10, the
correlational square amplitude calculation value of the record to
be compared with "X" is larger. Therefore, the records stored at
the addresses "X" through "X+3" are rewritten to be those at the
addresses "Y" through "Y+3". As a result, the records originally
stored at the addresses "X" through "X+3" are overwritten and
erased. Next, the records at the address Y+4 and the subsequent
addresses are moved ahead to the address Y and the subsequent
addresses, Namely, since the records previously stored at the
addresses "X" through "X+3" are erased, the storage locations of
the records at the address "Y" and the subsequent addresses are
moved ahead by 1 entry. AT the same time, the records at the
address "Y" and the subsequent addresses "Y+3" are overwritten to
prevent the identical data from existing duplicately. In step S13,
"4" is subtracted from the variable "DataEnd" indicating the last
entry address of the latest storage records. After the process in
step S14 is performed, the flow goes back to step S4 and the above
described process is repeated. The process in step S13 is intended
to move ahead also the entry address of the last record in
correspondence with the process for overwriting and erasing the
records at the addresses "X" through "X+3", and the process for
moving ahead the storage locations of the records at the address
"Y" and the subsequent addresses by 1 entry, which is performed in
step S12.
With the above described processes, only the record having the
maximum correlational square amplitude calculation value is left
sequentially from the timing data having a larger correlational
square amplitude calculation value, and the remaining records are
sequentially deleted. Finally, only the record in which the maximum
correlational square amplitude calculation value is set is stored
for each timing data in the storing circuit 36. Additionally, these
records are stored in descending order of a maximum correlational
square amplitude calculation value.
In the example shown in FIG. 13, for the records having the timing
"50", the record at the entry address "DataStart" is left, and the
records at the entry addresses "DataStart+4" and "DataStart+8" are
deleted. Additionally, for the record having the timing "75", the
record stored at the entry address "DataStart+12" is left and the
other record is deleted. Then, the record stored in the entry at
the address "DataStart+12" is stored in the entry at the address
"DataStart+4". The records having the maximum correlational square
amplitude calculation value for each timing, which are not shown in
this figure, are moved ahead also in the respective entries at the
address "DataStart+8" and the subsequent addresses.
The process shown in the above described flowchart is merely one
example. A plurality of methods for determining whether or not the
record stored in the storing circuit 36 is the record of the signal
from the same base station, can be considered. For example, an
arbitrary entry record may be deleted using a random number without
leaving a larger correlational square amplitude calculation value
when the record of the signal from the same base station is
deleted.
FIG. 14 is a block diagram showing the configuration of a mobile
station according to an eighth preferred embodiment of the present
invention.
In this figure, the same constituent elements as those shown in
FIG. 11 are denoted by the same reference numerals.
This preferred embodiment is a configuration for easily realizing
the capabilities of the seventh preferred embodiment on a mobile
station side. That is, in the seventh preferred embodiment, its
process is performed by estimating the signals transmitted from the
same base station to have the same timing. Actually, however, the
signals may have different timing at respective frequencies even if
they are transmitted from the same base station. This preferred
embodiment assumes the case where each base station shifts the
phases of the common short codes in long code mask symbol parts of
perch channel signals at respective carrier frequencies, by a
predetermined value common to all of base stations (provides a
delay to the frequencies). The long code-masked symbol part is the
portion 103 which is spread with the common short code and the
group short code of the perch channel signal 100 in FIG. 1. Since
this portion 103 is not spread with a long code, that is, this
portion 103 is in a state where spreading with a long code is
maskted, it is referred to as the long code-masked symbol part.
Since the amount of a delay (a delay time?) provided between
frequencies is predetermined in such a system, the amount of a
delay to be provided to a received signal frequency can be decided
by predetermining which frequency is received.
The signal received by an antenna 20 is received by a receiving
circuit 21. A controlling unit 27 provides frequency specification
data to a receiving circuit 21 and converts a particular frequency
signal into an IF band signal. The converted IF band signal is
input to an orthogonal demodulator 22, which demodulates the signal
into an I and Q signals. After the I and Q signals are respectively
converted into digital signals by A/D converters 23-1 and 23-2,
they are input to matched filters 24-1 and 24-2. Then, the
correlation values between a common short code and the digital I
and Q signals are calculated by the matched filters 24-1 and 24-2.
Then, the correlational power value based on the correlation values
is calculated by a square amplitude calculating circuit 25.
Frequency specification data is output from the controlling unit 27
to switches SW1 and SW2, which determine whether or not the output
from the square amplitude calculating circuit 25 is input to a
delay element 40 by using the frequency specified by the frequency
specification data. Because the amount of a delay provided to
respective carrier frequencies is predetermined at all base
stations, the carrier frequency signal having a maximum delay is
input to a CPU 35 without being passed through the delay element
40. The correlational power values of other carrier frequency
signals are input to the delay element 40 by turning on/off the
switches SW1 and SW2, so that their delay amounts are cancelled.
The frequency specification data output from the controlling
circuit 27 is also input to the delay element 40. The delay element
40 determines how much the currently selected carrier frequency
signal is delayed from the carrier frequency signal having the
maximum delay, and changes the timing at which the correlational
power value output from the square amplitude calculating circuit 25
is input to the CPU 35 based on this determination in order to
adjust the amount of a delay from the signal having the maximum
delay to be "0". Additionally, the frequency specification data is
input to the CPU 35, and the records like those shown in FIG. 13
are stored in a storing circuit 35 in a similar manner as in the
above described preferred embodiment.
As described above, all of the timing at which the correlation
power values of respective carrier frequency signals transmitted
from the same base station are input to the CPU 35 become identical
even if the carrier frequencies are different. This is because the
delay amounts of the respective carrier frequencies are cancelled.
Accordingly, the data processing based on the estimation such that
the input timing of the correlational power values of the signals
transmitted from the same base station become identical, can be
used when the data stored in the storing circuit 36 is processed,
as referred to in the explanation about the seventh preferred
embodiment. Namely, with the configuration according to this
preferred embodiment, the process of the flowchart shown in FIG. 11
can be applied unchanged even if the signals transmitted from one
base station have different timing at respective carrier
frequencies.
The CPU 35 then passes a frequency and timing candidates of a perch
channel signal to the controlling unit 27, and makes the
controlling unit 27 perform a cell search.
In this preferred embodiment, the delay amounts of frequencies are
corrected by using the switches SW1 and SW2 and the delay element
40. However, the delay correction is not limited to this
configuration. Data delay amounts may be corrected by the software
processing of the CPU 35 after correlational power values are once
stored in the storing circuit 36.
By the way, the delay amounts (offset chip amounts include "0",
that is, no delay (offset).
A preferred embodiment to be explained below is intended to prevent
a new user from subscribing to a frequency at which traffic is
heavy and to promote a new user to subscribe to a frequency at
which traffic is light by combining the mobile station/cellular
system according to the preferred embodiments explained so far, and
a base station having a capability for obtaining the congested
state of the traffic within a cell, and by changing the
transmission powers of the frequencies at which their traffic are
heavy and light. Additionally, since a user capacity is determined
by an interference power between channels in a CDMA cellular
system, this preferred embodiment can be used to suppress a new
subscription when the interference power within a cell becomes
equal to or higher than a predetermined level. If a single
frequency cell suppresses a newly subscribing user when many
frequency cells are controlled by one base station, the new user
naturally subscribes to any of the other frequency cells which does
not suppress new users.
FIG. 15 is a block diagram showing the configuration of a base
station according to a first preferred embodiment of the present
invention.
This figures shows the configuration of a transmitting station. As
shown in this figure, transmitting units 50-1, 50-2, . . . , which
respectively generate a signal at a different frequency, are
arranged in parallel. Signals output from the transmitting units
50-1, 50-2, . . . are coupled prior to a power amplifier 46, and
the coupled signal is amplified by the power amplifier 46. The
amplified signal is then transmitted from an antenna 45.
Because all of the fundamental configurations of the transmitting
units 50-1, 50-2, . . . are identical except for a difference in
the frequencies of output signals, only the internal configuration
of the transmitting unit 50-1 is shown. Each of the transmitting
units 50-1, 50-2, . . . obtains the number of users accommodated in
its frequency from a managing device in a CDMA cellular system,
which is not shown, and inputs the obtained number to a controller
49. Additionally, also the data to be transmitted from a base
station is input to each of the transmitting units 50-1, 50-2, . .
. , and is modulated by a modulator 48. The modulated data is input
to a digital control type attenuator 47 (not limited to a digital
control type). The attenuation amount of the digital control type
attenuator 47 is controlled by an attenuation amount control signal
that the controller 49 generates based on the number of users in a
corresponding frequency. By increasing the attenuation amount of
the frequency in which many users are accommodated and decreasing
the attenuation amount of the frequency in which few users are
accommodated within the transmitting units 50-1, 50-2, . . . , the
signal having the frequency in which few users are accommodated is
transmitted with great strength. In this way, when a mobile station
comprising a receiving device according to any of the first through
the eighth preferred embodiments is used, many new users are
accommodated in a frequency where few users are accommodated when
using a mobile station comprising a receiving device according to
any of the first through the eighth preferred embodiments. Assume
that the transmission power of a perch channel at a frequency whose
traffic is heavy is "P1", and the transmission power of the perch
channel at the frequency whose traffic is light is "Pg". If
P1>Pg is satisfied at this time, the probability that most new
users within a service area subscribe to the frequency whose
traffic is light becomes high. If "P1" is set to be sufficiently
large for "Pg", it becomes possible to accommodate most of the new
users in a cell whose traffic is light.
This implementation is for the case where the transmission power of
a perch channel at a single carrier frequency is controlled. A
modulation operation such as spreading, etc. is performed for the
data transmitted on the perch channel, and its transmission power
is adjusted by the controller 49 with the attenuator 47 which can
control the attenuation amount. Then, the data signal is amplified
by the power amplifier 46 and is transmitted. The number of
transmission users within the cell is input to the controller 49 as
data, and the attenuation amount of the attenuator 47 is determined
with this data.
Additionally, if the level of a common short code in a perch
channel signal in a certain carrier frequency cell is sufficiently
lowered and if the remaining portion of the perch channel signal
except for the common short code portion is transmitted and left
unchanged, no more users can newly subscribe to the cell. If the
base station sets the power of the common code spread signal in a
perch channel signal of a different carrier frequency for the cell
to a power higher than the power of the certain carrier frequency
spread signal at this time, most new users subscribe to the cell
having the carrier frequency at which the transmission power of the
common short code is higher. Considering noise, interference, etc.,
100 percent new users do not always subscribe to the cell having
the carrier frequency at which the transmission power of the common
short code spread signal is higher. However, this tendency grows as
the difference between the transmission powers increases. If a
mobile station requires a common short code spread signal at the
time of handover to a certain cell, it becomes possible to disable
the handover to the cell. It doesn't matter if a user currently
existing in the cell requires the broadcast information (spread by
a signal other than the common short code) about a perch channel
signal during a call in this case, because this information is
continuously broadcast.
Furthermore, the above described implementations are available also
to a base station which physically separates and accommodates cells
having different carrier frequencies. For example, many mobile
stations temporarily concentrate in a particular area in some cases
when an event such as a festival is held. In such a case, problems
such as a difficulty in making a telephone call, a degradation in a
speech quality, etc. can possibly occur because the accommodation
capacity of an existing base station is exceeded. When the number
of users reaches a predetermined number at an existing base station
in this case, the power of the common short code spread signal is
minimized (reduced to "0" if possible) and the power of the short
code spread signal at a base station arranged on demand is
transmitted at a normal level, thereafter, most users come to
subscribe to the cell at the base station arranged on demand. As a
result, the problems such as a difficulty in making a telephone
call and a degradation in a speech quality can be prevented from
occurring. There is an advantage to a mobile station that the
initial cell search time does not increase. Additionally, this
method is available for the system where a perch channel exists in
a single frequency although the system itself uses a plurality of
carrier frequencies. In this case, a mobile station makes an
initial cell search for the single frequency.
FIG. 16 is a block diagram showing the configuration of a base
station according to a second preferred embodiment.
This figure assumes only "f1" and "f 2" to be the frequencies used
by the base station. However, the number of frequencies used by the
base station is not always limited to two.
This preferred embodiment is intended to independently control only
the transmission power of a common short code spread signal on a
perch channel. Remaining data except for the long code-masked
portion on the perch channel is orthogonally multiplexed by
orthogonal modulators 56-1 and 56-2, and the multiplexed data is
spread with a common short code by short code spreading units 58-1
and 58-2. The common short code is spread (despread) with a long
code by long code despreading units 57-1 and 57-2, weighted
(amplified with gains "g1" and "g2") by amplifiers AMP1 and AMP2,
and time-multiplexed with the data output from the short code
spreading units 58-1 and 58-2. Here, adders 59-1 and 59-2 perform
an exclusive-OR operation. The time-multiplexed signal is spread
with the long code by long code spreading units 60-1 and 60-2. A
transmitting unit 55-1 frequency-converts the signal spread with
the long code into a signal having a frequency "f1", and outputs
the signal. In the meantime, a transmitting unit 55-2
frequency-converts the signal spread with the long code into a
signal having a frequency "f2", and outputs the signal. The signals
having the frequencies "f1" and "f2" are coupled by a coupling unit
54, and power-amplified by a power amplifier 53. Then, the
amplified signal is transmitted from an antenna 52.
The reason that the common short code is spread with the long code
by the long code spreading units 60-1 and 60-2 after being despread
with the long code by the long code despreading units 57-1 and 57-2
is to prevent the long code-masked portion from being spread with
the long code. Namely, the common short code is spread with the
long code after being despread with the same long code, so that the
long code is cancelled and the common short code itself is
output.
The gains "g1" and "g2" of the weighting of the amplifiers AMP1 and
AMP2 are determined according to the number of users within a cell
in the controlling unit 62. The number of users within a cell is
obtained from the notification from an intra-cell user number
counting unit 63 arranged as a user monitoring capability of a CDMA
cellular system. That is, the gains "g1" and "g2" of the amplifiers
AMP1 and AMP2 within the transmitting units 55-1 and 55-2 having a
frequency in which a large number of users within a cell is
accommodated are decreased, while the gains "g1" and "g2" of the
amplifiers AMP1 and AMP2 within the transmitting units 55-1 and
55-2 having a frequency in which a small number of users within a
cell is accommodated are increased. If orthogonal modulation is not
performed, the orthogonal modulators 56-1 and 56-2 shown in FIG. 15
are unnecessary. Additionally, if a perch channel is arranged in a
single carrier wave frequency depending on a system, only one
transmitting unit is sufficient to implement this preferred
embodiment.
Or, not the number of users, but a signal-to-interference power
ratio, a signal-to-(interference+noise power) ratio, an
interference power, or an interference+noise power can be used.
These items of information can be measured with a known technique.
These information are input to the controlling unit 62 instead of
the number of users in such a case. That is, the number of users
that can be accommodated within a cell depends on the level of an
interference power or a noise power. Therefore, the gains "g1" and
"g2" can be adjusted to allow the maximum number of users to be
accommodated in a cell without exceeding the number of users that
can be accommodated within the cell.
A transmission-to-interference power ratio base station side
measuring unit or an interference power measuring unit, which is
intended for controlling a transmission power of a CDMA cellular
system, is made common to that used in this preferred embodiment,
thereby reducing hardware amount, an operation amount, and a
consumption power.
FIG. 17 is a block diagram showing the configuration of a base
station according to a third preferred embodiment of the present
invention.
In this figure, the same constituent elements as those shown in
FIG. 16 are denoted by the same reference numerals.
This preferred embodiment is intended to control the transmission
power of a perch channel signal in each carrier frequency at a base
station according to the number of users within a visited cell, or
to control the base station transmission power of the signal spread
with the common short code within a perch channel signal in each
carrier frequency. In this case, the above described transmission
power is controlled according to an average traffic volume
including potential traffic. Namely, the base station according to
the second preferred embodiment determines the gains "g1" and "g2"
of the amplifiers AMP1 and AMP2 based on the number of users that
actually access the base station. However, according to the third
preferred embodiment, a base station determines the gains "g1" and
"g2" of amplifiers AMP1 and AMP2 based on the number of users
existing within a cell that the base station itself covers. For
example, a controlling unit 62 can learn the number of users to be
accommodated by the local base station from the number of users
within a visited cell. Therefore, the gains "g1" and "g2" of the
amplifiers AMP1 and AMP2 are controlled to allocate the frequency
channels possessed by the local base station to the users as
efficiently as possible. For example, if the users are evenly
accommodated in all of the frequencies possessed by the local base
station, the amplifiers AMP1 and AMP2 are switched to increase the
gains at predetermined time intervals. As a result, the channels
used by the visiting users can be allocated almost evenly.
With the configuration according to this preferred embodiment,
after the number of users within a visited cell is obtained, it is
compared with the number of users within a visited cell of a
different station. If many mobile stations exist in a cell of a
next base station and if few mobile stations exist in a cell of a
local base station, the gains "g1" and "g2" of the amplifiers AMP1
and AMP2 are increased to accommodate the mobile stations existing
in the cell of the next base station in the local base station. In
this way, the situation where many mobile stations access a
particular base station, which cannot accommodate all of the mobile
stations, can be prevented.
Since the number of users within a visited cell is normally stored
in a CDMA cellular system visit location register outside a base
station, the number is read from this register. Unlike a normal
visit location register, the visit location register according to
this preferred embodiment also grasps in which base station area
each mobile station stays.
The transmission data in the portions except for the long
code-masked portions are orthogonally modulated by orthogonal
modulators 56-1 and 56-2, and spread with a common short code by
short code spreading units 58-1 and 58-2. Then, these portions are
spread by long code spreading units 60-1 and 60-2, and
frequency-converted into signals having respective frequencies. The
frequency-converted signals are coupled by a coupling unit 54, and
the coupled signal is transmitted from an antenna 52 via a power
amplifier 53. After the portions of the common short code in the
long code-masked portions are despread with a long code by long
code despreading units 57-1 and 57-2, they are amplified with the
gains "g1" and "g2" by the amplifiers AMP1 and AMP2. The amplified
signals are time-multiplexed with the data from the short code
spreading units 58-1 and 58-2 by adders 59-1 and 59-2, and are
spread by the long code spreading units 60-1 and 60-2. After the
spread signals are frequency-converted into signals having
respective frequencies, they are coupled by the coupling unit 54,
and the coupled signal is transmitted from the antenna via the
power amplifier 53.
FIG. 18 is a block diagram showing the configuration of a base
station according to a fourth preferred embodiment of the present
invention.
In this figure, the same constituent elements as those shown in
FIG. 17 are denoted by the same reference numerals.
According to this preferred embodiment, the measurement result of
an upward signal-to-interference power ratio, a
signal-to-(interference power+noise) ratio, an interference power,
or an interference+noise power at a base station is averaged, and
the averaged value is used to control the transmission power of a
transmitting unit having each frequency in a CDMA cellular
system.
Especially, in the configuration shown in FIG. 18, the weight of a
common short code is determined by a controlling unit 62 based on
the average of the measurement value of a wireless line
signal-to-interference power ratio at each frequency at a base
station. This wireless line signal-to-interference power ratio is
also used to control the upward transmission power of each wireless
line. An SIR measurement method is already known. Also the
configuration for measuring Eb/IO can be implemented instead of the
SIR.
Namely, the signal-to-interference power ratios (SIRs) measured by
a wireless line 1 SIR measuring unit 66-1 through a wireless line N
SIR measuring unit 66-N are averaged by an averaging unit 65 for
each frequency, and the obtained data is provided to a controlling
unit 62. The controlling unit 62 performs control so as to decrease
the amplification gain of the amplifier for a transmitting unit 55
having the frequency whose SIR value is large, and to increase the
amplification gain of the frequency whose SIR value is small based
on the averaged SIR data for each frequency input from the
averaging unit 65. As a result, the frequency whose SIR value is
large, that is, the frequency of a low communication quality
accommodates only a few users, while the frequency whose SIR value
is small can accommodate many users. As a result, a service of a
high communication quality can be provided as a whole.
Since other configurations and operations according to this
preferred embodiment are similar to those of the above described
base stations according to the second and the third preferred
embodiments, their explanations are omitted here.
Additionally, the above described mobile station and base stations
according to the preferred embodiments of the present invention can
also be applied to a system having a single carrier frequency. A
mobile station is assumed to select the cell whose common short
code reception level is the highest as a visited cell as referred
to in the conventional technique. If the transmission power of the
common short code spread signal on the perch channel at a certain
base station is set to a level lower than that of a peripheral base
station at a single carrier frequency, the mobile station
subscribes to the cell of the base station whose transmission power
of the common short code is higher. As a result, a subscription to
a particular base station can be restricted. On the other hand, if
the transmission power of the common short code spread signal on
the perch channel at a certain station is set to a value higher
than that of a peripheral base station, a subscription to the perch
channel can be promoted. In this case, some users peripheral to the
base station whose transmission power is lowered subscribe to the
cell of a base station peripheral to that base station. Because the
respective preferred embodiments according to the present invention
are applied to a system having a single carrier frequency by using
only a single carrier frequency in the configurations of the
respective preferred embodiments, their detailed explanations are
omitted here. In such a system, a mobile station may make a cell
search at a single frequency as indicated by the conventional
technique.
The above explanation is simplified and provided in such a way that
only a common short code is the code input to the long code
despreading units 57-1 and 57-2 in the base stations according to
the second to the fourth preferred embodiments of the present
invention. Actually, however, a common short code and a group short
code are combined and input.
According to the present invention, a mobile station can access the
most suitable channel of a base station, and at the same time, the
base station can control the channel that the mobile station
accesses according to the allocation status of mobile stations in a
spread communication system, whereby an efficient communication
service can be provided while maintaining a communication
quality.
* * * * *